1. Field of the Invention
This invention relates to novel synthetic abrasive stones based on a novel foamed glass composition and method for making the same based on waste glass, foaming agents, binders and mixtures thereof. This invention also relates to the novel use of said synthetic abrasive stone to replace pumice in the process known as "stone-washing" as used in the garment industry. Pumice is added to the washing process to soften, and abrade, the fabric, and to impart variations in the appearance of the fabric. Pumice is often impregnated with bleach and various chemicals which are released during the washing cycle to create variations in the appearance of the fabric. This process results in treatments of fabric known to the industry as "acid washed", "ice washed", "electric washed", etc.
There are many disadvantages associated with the use of pumice for stone washing. 1) Mined pumice varies widely in its density, abrasive qualities, absorptive qualities and in the size of the stones, making it difficult to maintain a supply of consistent material to the industry. A wide range of these variations occur from mine site to mine site and often times within one site. 2) Locations of pumice that are deemed suitable by the garment industry are very limited. The majority of the pumice used by the industry is imported from Turkey, Greece, Ecuador, and Indonesia, at great expense. 3) Great environmental damage results from strip mining pumice. 4) Due to the high attrition rate of pumice in the stone washing process, the broken down pumice or sludge must be trapped and then hauled to a land fill at great expense. As a result of the problems associated with using pumice for stone washing, there has been a growing demand for a consistent less expensive replacement material. This has resulted in much experiment ranging from the use of bottle caps to pumice grit mixed with cement. These attempts have proved to be largely unsuccessful.
Foamed glass can be made into synthetic abrasive stones and can be used as a substitute for the pumice that is currently used by the garment industry, resulting in better abrasion, lower attrition rate, good absorptive properties, and significantly lower cost. The desirable properties of foamed glass can be widely varied and manufactured with consistency to meet the garment industry's needs. Foamed glass can also be molded into a block to fit over the agitation fins of the washing machine which would further lower the attrition rate and eliminate the need to pick pumice out of the pockets of the finished garments. The trapped grit or sludge resulting from the use of foamed glass synthetic stones for stone washing can be remade into said stones. Synthetic abrasive stones made from waste glass can provide a significant market for recycled glass, which is currently very limited.
2. Prior Art
Foamed glass has long been known as a heat and sound insulating material. Prior art in this field is extensive and has been the subject of many patents. The National Technical Information Service, Publication No. AD/A-05 819, Demidevich, Manufacture and Uses of Foam Glass, discloses many methods for making foamed glass and foamed glass compositions utilized throughout the world up through 1972. The subject of most of the patents and research in the field relates to improved methods of manufacture and improved glass compositions. The object of these improvements is to produce a material that is extremely low in density, that provides for good heat and sound insulating properties, is impervious to water, and is acid resistant. Other uses of foamed glass relate to a skin or glazed surface composition used as a building facing material, an aggregate or filler material used in construction products, the making of blocks or tiles for construction purposes, and as a filtering material.
It has been found that foamed glass pellets or stones, produced by known means and comprising foaming agents within disclosed ranges, i.e., 0.05% to 2% on up to the extreme range of 10% claimed by Mackenzie, U.S. Pat. No. 3,963,503, are entirely unsuitable for stone washing as they have an attrition rate that is even higher than pumice or they significantly damage the fabric or both (see subsequent Examples 13 and 14).
Foamed glass can be produced utilizing many methods of production and numerous glass and foaming agent compositions. These include, by way of example only, glass compositions comprising waste glass (including waste foamed glass), soda lime glass, borosilicate glass or aluminosilicate glass, and foaming agents such as carbonates and sulfates of the various alkali and alkaline earth metals such as calcium carbonate, potassium carbonate, sodium carbonate, barium carbonate, strontium carbonate and the like, and calcium sulfate, potassium sulfate, sodium sulfate, barium sulfate, strontium sulfate and the like as well as carbon black, sulfur, dolomite and the like.